1. Field of the Invention
The present invention relates to an organic electroluminescent display panel used in a display apparatus and comprising a plurality of organic electroluminescent elements (also referred to herein as EL elements) each including an emitting layer made of an organic compound material, which utilizes an electroluminescence phenomenon that is the emission of light resulting from injection of an electric current to the emitting layer. More particularly, it is related to a full color display device comprising a matrix of the EL elements.
2. Description of the Related Art
Generally, the formations of the cathode and the organic function layers of EL media in the organic EL element are difficult in a micro-patterning art, since there are the low levels in durabilities of heat resistance (100.degree. C. or less), wet-proof and solvent-resisting of the organic EL media used for the carrier injection layers, the emitting layer or the like in the function layers. If the ordinary photolithography patterning is utilized for the formation of such function layers of the organic EL element, the solvent in the photoresist infiltrates into the function layers of the EL element, to be damaged, and the organic EL element is damaged during the photoresist baking with a high temperature atmosphere, and further, the development solution or etching liquid for the photoresist layer also intrudes into the organic EL element, to be damaged. Even plasma in the dry-etching for the photoresist layer damages the organic function layers of the EL element. These damages cause the deterioration in the performance of the organic EL element and emission properties. This is a serious problem.
Alternatively, there is a vacuum deposit patterning by using a shadow mask to form the cathode and the organic function layers of the organic EL element. In this case, there are many problems in that the mask comes into contact with a substrate on which the organic function layers are formed. That is, the leakage of the vapor of organic EL media occurs between the mask and the substrate due to incomplete contact thereof. Otherwise, the shadow mask is compulsorily, sealingly put into contact with the substrate. In this case, the organic EL medium is damaged due to the contact of the forced mask during the EL medium deposition, and further the cathode to be deposited is deformed by the mask, to be short-circuited to the anode made of indium tin oxide (referred to herein as ITO) previously formed on the substrate. This direct contact of the mask and the substrate further causes deformities of the mask with precise fine patterns such as stripe cathode patterns because of insufficient strength of the mask with such stripe openings. Therefore, it is very difficult to form precise fine patterns for the cathode and the organic function layers of the organic EL element.
As full color display devices, there have been known emitting devices as shown in Japanese Patent Kokai Nos. 2-66873, 5-275172, 5-258859 and 5-258860, the latter of these three corresponding to U.S. patent applications Ser. Nos. 814512, 814163 and 814553 respectively. Each full color display device comprises a plurality of emitting pixels existing at intersections of lines and rows of matrix electrodes.
In the emitting device, the pixels are formed on a common transparent substrate with electrical insulation. The line electrodes made of transparent material are formed on the substrate and spaced from one another. These first transparent electrodes connect the adjacent pixels. Organic EL media are formed on the first electrodes and the substrate. The pixels include the second electrodes of row formed on the organic EL media respectively and spaced from one another. The second electrodes of row extend perpendicular to the first electrodes and connect the adjacent pixels respectively. In the emitting device, there is employed a simple matrix structure that the first and second electrodes sandwich the organic EL media at the intersections thereof.
Japanese Patent Kokai No. 2-66873 discloses a technology to avoid the forgoing problem of the infiltration of the photoresist solvent into the EL medium layer, that is, the photoresist comprising a specific solvent non-melting the organic EL medium is used in the photolithography patterning, and then the cathode pattern is etched by a dilute sulfuric acid to form the cathode. However, such an etching step is a problem in that the dilute sulfuric acid damages the previously formed organic EL medium layers on the substrate.
In the technology disclosed in Japanese Patent Kokai Nos. 5-275172, 5-258859 and 5-258860, such an emitting device is manufactured as follows: Straight higher walls with a height of several or tens micrometers as masks are previously formed on the substrate. The second electrodes and the organic EL medium thin films are vacuum-deposited by using such higher wall masks in such a manner that a predetermined organic EL medium vapor flow is provided in only one slanting direction to the substrate and partially and selectively shielded by the higher wall masks.
However, such a method restricts the flexible layout of pattern of pixels within a stripe shapes, since the wall masks must be formed perpendicular to the only one slanting direction of the organic EL medium vapor flow. Therefore, it is impossible to form a pixel pattern with a delta arrangement RGB in the panel nor any display panel with a bent or meandered cathode pattern.
Further, it is still difficult to form such higher wall masks on the substrate when fine pixels and patterns are fabricated for the full-color display panel, i.e., in detail it is very difficult to form the higher wall mask having a high aspect ratio (height/bottom) in its cross-section. Even if such higher wall masks are formed on the substrate, the strength of the wall will be low and the reliability in the performances and shapes of the resulting second electrodes and organic EL media films will be low. In addition, such a manufacture of the emitting device invites a complicated processing because of the slanting vapor flow deposition in one direction with a low precision.